negatively regulates synapse assembly negative regulation of nervous system development regulation of synapse assembly negative regulation of synapse assembly negative regulation of synaptogenesis biological_process down regulation of synapse assembly downregulation of synapse assembly negative regulation of synapse biogenesis GO:0051964 down-regulation of synapse assembly Any process that stops, prevents, or reduces the frequency, rate or extent of synapse assembly, the aggregation, arrangement and bonding together of a set of components to form a synapse. biological regulation negative regulation of cell junction assembly negative regulation of synapse organization